1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. For example, in electron beam writing, the present invention relates to a method of correcting for pattern dimension variation due to a phenomenon whose influence radius is less than that of a proximity effect, like the case of extreme ultraviolet (EUV) short range proximity effect correction (PEC).
2. Description of Related Art
The lithography technique that advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. In order to form a desired circuit pattern on semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high precision is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a highly precise master pattern.
FIG. 10 is a schematic diagram explaining operations of a variable shaped electron beam writing apparatus. As shown in the figure, the variable shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g. x direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture plate 410 and the variable-shape opening 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) method.
In the above-described electron beam writing, highly precise uniformity of the line width is required on the surface of a target object, such as a mask surface, when writing a pattern on the target object. However, in the electron beam writing, a phenomenon called a proximity effect occurs when electron beams irradiate a circuit pattern on a mask with resist to write a pattern. The proximity effect is generated by the backward scattering of electron beams penetrating the resist film, reaching the layer thereunder to be reflected, and entering the resist film again. As a result, a dimension change occurs, thereby causing a written pattern deviated from a desired one in dimension. On the other hand, when developing or etching after writing a pattern, a dimension change called a loading effect due to density difference of a circuit pattern occurs.
Here, there is a proximity effect correction coefficient η which is suitable for performing proximity effect correction, for each base dose Dbase. Then, a method of calculating a dose for correcting a dimension variation amount due to a loading effect while correcting a proximity effect along with changing a combination of the base dose Dbase and the proximity effect correction coefficient η is disclosed (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2007-150243).
However, with the recent miniaturization of patterns, it has turned out that an error occurs in a conventional dose calculation model in accordance with downsizing of a pattern to be written. For example, it has turned out that an error occurs in a conventional dose calculation model with respect to a phenomenon whose influence radius is several μm or less, like the case of EUV short range proximity effect (short range PEC). The influence radius of such phenomenon is less than that of the proximity effect described above.
If calculating a dose including such deviation all from the start, the time for processing will be very long since all the writing regions need to be calculated in a unit of a small region. Therefore, for example, it can be considered to calculate an amount of correction in advance at the outside before performing writing and to define the calculated correction amount as additional data of layout data to be input into a writing apparatus. However, there is a problem that such a method cannot be used when needing to change the parameter for correction calculation. Thus, although it is desirable to perform correction calculation more simply in a writing apparatus, an adequate method for solving the problem described above has not been established yet.